Michael
> Incidentally, if you replace \emph{et al.} by {\it et al.}, it does work
> properly.
>
Coincidentally(??) this aside provides the clue as to why the spurious
`, ' appears.
The problem was that, in the bad redefinition, in effect both an \hbox
_and_ a TeX group (from the pair of {}) had been removed.
The TeX group was there for protection against some non-defensive
internal programming using one temporary local switch for two purposes,
one in \cite and one in \emph. Putting the \emph in a group prevents
any interference.
Many apologies for not documenting in the sources the importance of
this group (did you look at ltbibl.dtx before chnaging it?).
Thaks for taking the time to advertise this. We shall continue to
search the code for similar programming slips.
Chris Rowley --- On behalf of the LaTeX3 Project Team